Stay-bolt connection for fire-boxes of boilers



Patented Apr. 12, 1932 I UNITED ST T EDUARD JoLLEnBEcK, or BERLIN, GERMANY STAY-BOLT CONNECTION marina-Boxes or BOILERS,

Application filed March 24, 1930, Serial No. 438,611, and in Germany August '9, 1929.

In locomotive, portable and other boilers provided with fireboxes having inner and outer Walls connected together by staybolts, the unequal'heating of the said walls results in stresses which may attain such dimensions that, despite the employment of copper for 'the'inner wall, the connections become leaky and fissures occur at the staybolts and in the plates. 1

To minimize leakiness and the performance of repairs on the side next the fire, it has 3.1-. ready been proposed to screw the staybolts in socket holes in the inner wall andto rivet them on the outside only.

In comparison with the usualpractice of providing two rivet heads, this arrangement afiordscertain advantages,but it does not take practical conditions into consideration, and

therefore cannot satisfy the essential requirements that a reliable and perfect staybolt connection must fulfill.

As the bolts are not elastic, they are unable to follow the unequal expansions produced by heat, and therefore the socket holes 5 in the inner wall become oval in time, and this change of form progresses as time goes on, with the result that the water of the boiler can find its way into the threads, with forma- V tion of oxide or rust and deposition of boiler fur. In this manner the threads become more and more corroded, so that the bolts (having no heads on the inner wall) lose their hold and can be torn out.

" the outer wall, the inner end of the staybolt should be screwed right into the bottom of the socket, but since this is technically'impracticable, the bolt does not find any firm abutment in the socket during the forming of the rivet 40 head. Consequently, the threads in the socket already begin to suffer damage during that.

operation and, in some cases, are even partially stripped, thus again greatly facilitating the penetration of the boiler water and '45 the attendant destruction of the staybolt connections.

The risk of damaging the threads of the socket is still further increased by the circumstance that, in forming the rivet head on the outer wall, it is very diflicult to find the found practical application because,

In order properly to form the rivet head oncorrect spot on the inner wall at'whi'ch'to apply the requisite support in riveting.

Finally, every bolt that is'driveninto'the bottom of the socket, or as far as the incompleted finalturns ofthe thread, altersf'the position of the inner wall and therefore that of the threads in the neighbouring portions of the wall, thus making screwing in of'other bolts difficult or impossible.

It follows that all'the'measuresand prescriptions directed to the attainment of the great-est 'possible'ac curacy in the production of the staybolts and screw'threadsyfailto accomplish their object so long as there is" no possibility of preventing the threads from being destroyed during the driving homeof the bolts and the forming of the rivet-head.

To render'the 'staybolt's more elastic,*it has also been proposed to give the unthreaded middle portio-n of the bolt a particularly flexible (for example, slotted) cross-sectional Such staybolts, however, have not if screwed into through holes, they would "beshape.

come-leaky sooner and to a greater extent-by reason of'their flexibility, quite apart from the'fac't that the slender design of the middle portion would make it impossible forthe 'bolt to be screwed tightly into the threads Moreover,-owing to "30 the necessity, in this case, offorming a-rivet head in the firebox, the weakened middle of the firebox plate.

portion of the bolt would become bent out of line, the inner plate would be dented round therivet head and the threads would be'damaged. v

' According to the present invention, "the defects attaching to the known staybolt connections are obviated by a combination of. the two known features, namely socket holes in the inner Wall and elastic stems the bolts. I v 1 As the thread of V the socket hole can be made with play at the point without consideration of tightness, the st'emof the bolt is not stressed in screwing up. Smce no rivet heads are employed in-"ma'kmg the connection, it is also unnecessary-for the inner end of the bolt to bescrewed right home in the socket. .Consequently, addi- I tional stresses and damage to the bolt, to the inner wall and to the threads is avoided, so that the accuracy obtained in making the bolts and the threads is retained during use.

A further result, especially when highgrade material is used, is that bolts can be made comparatively slender and therefore elastic, since they have only to absorb the load due to the boiler pressure.

This favourable effectis further intensified by forming the inner walls with undulations in accordance with a further development of the invention. In this manner the inner walls are rendered satisfactorily flexible, and accumulations of material required for the formation of the socket hole are provided on the water side of the inner walls. The shape and direction of the undulations are specially selected so as to ensure the circulation of the unoccupied by socket holes to assure uniform and rapid transmission of heat from the fire gases to the boiler water, by way of the inner wall, thereby preventing stresses and consequent fissuring.

According to the embodiment shown in Fig. 3, the inner wall 2 is of undulating design, which assures perfectly uniform stressing of the inner Wall.

I claim:

A stay-bolt connection for fire-boxes of boilers including a fire-box of uniformly wave-shaped conformation at its inner and outer surface, a stay-bolt having a resilient central part, a thread at the inner end of said stay-bolt, a threaded socket at a re-inforccd part of said wall of the fire-box and adapted for reception of said thread, a further thread at the outer end of said stay-bolt, and a threaded hole passing through the wall of the boiler and adapted for steamtight reception of said thread at the outer end of said staybolt without formation of a rivet head, said resilient central part of the staybolt together with said wave-shaped conformation of said wall of the fire-box permitting compensation of the mechanical strains imposed upon the several parts of the stay-bolt con nection during operation of the boiler.

In testimony whereof I have affixed my signature. 7

EDUARD JoLLENBEoK.

the staybolt along the line A-B of Fig. 1; V

and

Fig. 3 shows the undulating inner wall of the firebox. 7 As is evident from the drawing, the staybolt 1 (made, for example of ordinary, rustless or special steel and the like) is screwed into a threaded bore 4 in the outer wall 5 and, by means of its threaded end 6, into a screw socket 3 in the inner wall 2.

The inner wall must be strengthened (by means of the provision of sockets) in order to prevent the bolts (which have to stand the boiler pressure) from drawing out, but the employment of inner walls of uniform thickness, even if made of copper, would result in stresses due to unequal distribution of heat and readily leading to the formation of fissures. To prevent this, ribs 9 or the like are provided at the seats of the sockets and are arranged in such a manner as also to serve as guides to facilitate the circulation of the water and the carrying away of steam bubbles.

The result attained is that the inner wall is thick enough to enable socket holes of sufficient depth to be made whilst retaining an adequate wall thickness between the bottom of the sockets and the firebox, and yet the inner Wall is sufliciently thin in the portions 

